Auto merge of #107297 - Mark-Simulacrum:bump-bootstrap, r=pietroalbini

Bump bootstrap compiler to 1.68

This also changes our stage0.json to include the rustc component for the rustfmt pinned nightly toolchain, which is currently necessary due to rustfmt dynamically linking to that toolchain's librustc_driver and libstd.

r? `@pietroalbini`